The present invention relates to a sputtering target of nonmagnetic-particle-dispersed ferromagnetic material, and in particular relates to a target that can be efficiently subjected to sputtering with a DC (direct current) magnetron sputtering system by improving the PTF (pass through flux). The present invention further relates to a sputtering target of nonmagnetic-particle-dispersed ferromagnetic material which realizes stable sputtering and optimal deposition speed when forming a film by sputtering, minimal arcing during the sputtering, reduction in the particles (dust) and nodules caused by such arcing, high density, minimal variation in quality, and improvement of mass productivity.
In the field of magnetic recording, technology has been developed for improving the magnetic property by causing a nonmagnetic material to coexist in a magnetic thin film. As examples, there are technology for improving the soft magnetic property such as magnetic permeability by having fine particles of nonmagnetic material in the magnetic thin film, and technology for improving various properties of a magnetic recording medium such as coercivity by using the nonmagnetic material to block or weaken the magnetic interaction between the fine metallic particles in the magnetic thin film material. Although this kind of thin film material is prepared based on normal sputtering, it is necessary to simultaneously sputter nonmagnetic materials with insulation property or high resistance and ferromagnetic materials composed from metals of low resistance. This sputtering method is to make a positive electrode substrate and a negative electrode target face each other, and generate an electric field by applying high voltage or radio frequency between the substrate and the target under an inert gas atmosphere. Here, the sputtering method employs a principle where inert gas is ionized, plasma formed from electrons and positive ions is formed, the positive ions in this plasma collide with the target (negative electrode) surface to knock out the constituent atoms of the target, and the extruded atoms adhere to the opposing substrate surface to form a film.
Generally speaking, as the sputtering method, the RF (radio frequency) sputtering method or the DC (direct current) sputtering method may be used. However, in order to simultaneously sputter materials with significantly different resistance, the RF sputtering method capable of sputtering an insulator is often used. Nevertheless, not only is the RF (radio frequency) sputtering device expensive, it possesses numerous drawbacks such as inferior sputtering efficiency, large power consumption, complex control and slow deposition speed. If high power is applied to increase the deposition speed, the substrate temperature will rise, and there is a problem in that this will cause deterioration in the substrate and deposition material. Meanwhile, if the DC magnetron sputtering system which is capable of sealing the plasma in the vicinity of the target by disposing a magnet on the back side of the target and leaking magnetic flux from the target surface is used, the DC sputtering method will be able to achieve low power consumption, high speed deposition, and superior mass productivity in comparison to the RF sputtering method. In addition, it is generally said that the DC sputtering method is able to produce high-quality films since the influence of the plasma on the substrate is small.
Accordingly, a sputtering target for simultaneously sputtering a nonmagnetic material and a ferromagnetic material is also devised so that deposition can be performed with the DC magnetron sputtering system as much as possible. However, when adopting the DC sputtering method, the target itself needs to possess conductive property. Even if the target possesses conductive property, such target that contains large amounts of nonconductive materials such as oxide and silicide makes deposition based on the DC sputtering method difficult since the bulk resistance of the target will increase. Thus, a sputtering target has been devised to have a structure in which nonmagnetic materials such as oxide are finely and spherically dispersed. Nevertheless, even with this kind of devisal, there is a problem in that large amounts of particles are generated, and a problem in that the PTF (pass through flux) is low and the deposition speed is slow.
Some conventional technologies are introduced below. As one example, proposed is a method of performing mechanical ironing to alloy powder having an alloy phase prepared with the rapid solidification method, and ceramic-phase powder (refer to Japanese Patent Laid-Open Publication No. H10-88333). According to this method, it is possible to obtain a sputtering target for use in a magnetic recording medium by preparing alloy powder in which ceramic-phase powder is evenly dispersed in the alloy powder, and thereafter molding this by way of hot pressing.
As another example, proposed is Co-base alloy containing a silica phase in which the average width sought with the line segment method is in the range of 0.5 to 5 μm, as well as Cr and Pt phases (refer to Japanese Patent Laid-Open Publication No. 2004-339586). The silica powder in this case is obtained with a special method of high-temperature flame hydrolysis. Nevertheless, with respect to the materials obtained with the foregoing methods, in the former case (first example), the object is simply forming the particles homogeneously as much as possible, and in the latter case (second example), although a target texture distributed in a web shape is obtained, the existence of coarse grains can be observed in certain places. Based on these types of methods, it is assumed that particles will increase enormously upon forming a film based on sputtering as described later, which will be unfit as a target material.
Moreover, as an example of a magnetic target, disclosed are a CoPt-base sputtering target (refer to Japanese Patent Laid-Open Publication No. 2000-282229), and a sputtering target with improved PTF (refer to Japanese Patent Laid-Open Publication No. 2005-530925). Nevertheless, these documents relate to a metal (alloy) target, and do not face the problems encountered with a target in which nonmagnetic particles are dispersed.
Japanese Patent Laid-Open Publication Nos. 2009-001860, 2009-001861 and 2009-001862 disclose technology of improving the PTF (pass through flux) by using Co—Cr alloy powder, Co—Cr—B alloy powder or Co—Cr—Pt alloy powder having an average grain size of 20 μm as the raw powder, and causing the target texture to become a diplophase structure by suppressing the diffusion during the sintering process as much as possible. In the foregoing case, however, it is necessary to set the sintering temperature to be low and, consequently, such different problems as the density being low and particles being generated will arise. Therefore, there is a problem with those inventions that no improvement in target characteristics can be expected.
In light of the above, the present Applicant developed a high-density sputtering target of nonmagnetic-particle-dispersed ferromagnetic material, which is capable of reducing the generation of particles (dust) and nodules generated during the sputtering process and improving the mass productivity with minimal variation in quality, by improving such a phase that particles of nonmagnetic material are dispersed in a ferromagnetic material (refer to Japanese Patent Application No. 2006-006575). The present invention is a further improvement of the foregoing invention.